The invention includes a variable output power microwave generator and a broadly tuned microwave applicator that is connected to the generator though a length of coaxial cable.
Many chemical reactions are greatly accelerated by heating with a microwave field as compared to an open flame, oven or oil bath. Systems for microwave chemistry that are available from several manufacturers have the limitations of physical size, limited to reagent volumes greater than a few milliliters, require retuning of the applicator when the reagent mix is changed, and limit the users ability to monitor the progress of the accelerated reaction.
U.S. Pat. No. 4,681,740, Apparatus for the Chemical Reaction by Wet Process of Various Products illustrates a length of waveguide that is terminated with end panels made from a conductive material with the magnetron oscillator placed near at one end of the cavity and a provisions to place to insert samples near the other end of the cavity. The waveguide is provided with tuning screws to adjust the tuning of the cavity to the requirements of the sample.
Systems such as these are generally suitable for performing reaction on relatively large volumes of chemicals. However the combination of the magnetron with its required cooling system, the sample holder, and the overall packaging make them excessively large for many laboratory applications.
U.S. Pat. No. 5,308,944 illustrates a cavity applicator that can be coupled to a microwave generator either by waveguide or coaxial cable. The geometry of this cavity is varied by sliding walls proportionately to adjust for the sample container and sample volume.
The paper, “Evaluation of a Microwave Cavity for the Synthesis of PET Radio Pharmaceuticals”; C. S. Dence et al; Journal of Labeling Compounds for Radiopharmaceuticals, 1995, #37, page 115. shows a microwave power oscillator with fixed output power connected to a tunable circular cavity.